Efficient size and shape controlled synthesis of nanoparticles remains challenging for the nano-scale research field, especially in the synthesis of metal alloy nanoparticles. Alloy nanoparticles are highly interesting for their properties in catalysis, magnetic properties, opto electronic properties and their potential use in biomedical applications. Challenges in their synthesis have lately focused on shape and size control in order to obtain morphological uniformity. Several groups have reported on shape controlled batch synthesis using metal carbonyl complexes as CO donors as well as the use of gasses under pressure yielding octahedral and pseudo-octahedral shapes with long carbon chain amines as surfactants. These batch methods are not amenable to scaling up to an industrial scale synthesis.
Scaling the synthesis beyond a few milligrams while maintaining control of morphology has received less attention. For nanoparticles to become technologically and commercially viable, the need for a robust scalable synthesis is ubiquitous. Traditional batch slow heating or “hot injection” methods require solvents, surfactants and ligand with a high boiling point in order to reach the temperatures required for nucleation. Furthermore, they are difficult to scale, pose safety concerns and are often highly sensitive to impurities.
These demands are particularly true for platinum nanoparticles. Platinum nanoparticles are interesting due to their activity in the oxygen reduction reaction, especially when used in fuel cells. Due to the high cost of platinum alternatives such as alloys, nanoparticles with reduced platinum content are attractive provided they maintain a high catalytic activity. Also, pure platinum particles suffer from substrate poisoning in certain fuel cell applications. It is well known that nanoparticle size can greatly affect catalytic performance in terms of activity, chemoselectivity and stability. Typically the highest activity is linked to the smallest size by a surface to volume ratio argument. It has been shown though that larger sizes may in some cases be more active. All in all a synthesis that allows for selection of size by tuning reaction parameters and is scalable to industrial scale is therefore highly desirable.